I'm estimating a GLM with a continuous variable $X_1$, a dummy variable $X_2$ and the interaction term $X_1*X_2$.
After my understanding, when interpreting the coefficient of $X_1$ you should assume the value of zero for $X_2$, i.e. also for the interaction term.
Now a colleague suggested that if I skipped one of the main effects, then the interaction would not be a real interaction, i.e. I could simply interpret the coefficients of both - the remaining main effect and interaction term as if there was no interaction term in the model. I could not find any literature that supported this view. Is it correct?